The 7 Causes
1. pH is too high
Above 7.8 the water haze and chlorine stops working. Test pH first, every time. Lower it to 7.2–7.6, then reassess.
2. The filter is dirty or undersized
If the pressure gauge is high, or you haven't cleaned a cartridge in months, stop adding chemicals and clean the filter. After a green pool or a dust storm you may need to clean it twice a day until it holds.
3. Not enough chlorine
Early algae looks like cloudiness before it looks green. Test free chlorine. If it's near zero, shock at dusk and run the filter overnight.
4. Dead algae or leftover shock debris
After a green-pool treatment the water often goes grey-white. That's dead algae. Vacuum to waste, keep filtering, don't panic-add more chemicals yet.
5. Calcium or high TDS
Hard water plus high pH gives a milky look that clarifier won't beat. Test calcium hardness. You may need a partial drain, a sequestering agent, and pH control — see the calcium guide.
6. Poor circulation
A closed valve, a clogged pump basket, or 2 hours of pump time in February. Point return jets down and around. Run 8 hours in summer.
7. Phosphates, metals, or a failing sand bed
Less common, but real. Phosphates feed algae. Metals (iron, copper) can haze or tint the water. Old sand channels and lets fines through. If 1–6 are fine and it's still milky, take a water sample to a pool shop for a full lab-style test.
How to Clear It Once You've Found the Cause
- Fix the cause (pH, filter, chlorine, circulation).
- Run the filter continuously until you can see the floor.
- Then, and only then, a clarifier or floc can speed the polish. Floc drops everything to the floor — you must vacuum to waste afterwards.
Don't stack products. Clarifier + floc + shock + algaecide on the same afternoon is how you get foam, stains, and a bigger mess. One change, wait, retest.
When Cloudy Isn't "Just Chemistry"
If the surface is shedding (plaster dust after a new interior), or you can see a film that won't filter out, that's a renovation or warranty issue — not a bottle of clarifier. Same if the water is cloudy and the walls feel gritty with scale.
